Is it possible to get coronavirus again: what scientists know
'13.05.2020'
Source: Medusa
In South Korea, several hundred patients who had a coronavirus infection were reported who, after a few days and even weeks after recovery, showed a positive reaction when re-tested, writes "Jellyfish".
The head of the central clinical committee for disease control, O Mion-dong, however, believes that such observations are not caused by repeated infections, but merely demonstrate the presence of nucleic acid residues of destroyed viral particles in the human body.
PCR tests that are used to detect the virus in patient samples find the RNA of the virus, in whatever form it is presented there - to the extent, of course, as far as the sensitivity of the test allows. The test system doesn’t care if the live virus is present in the sample or destroyed. Thus, if the genetic material of the virus has not managed to be completely eliminated from the patient’s body, the test can give a positive result even if there are actually no virus particles capable of infection in the body.
Epithelial cells of the human respiratory tract can live for several months, adds O Mion-dong, and virus RNA can potentially be detected a month or two after the cell itself carrying the virus has already been destroyed by the immune system.
Earlier, in the Korean counterpart of Rospotrebnadzor (Korean Centers for Disease Control and Prevention, Korea Centers for Disease Control and Prevention), they tried to evaluate the infectiousness of such "secondary" patients and concluded that they apparently were not able to infect other people. At the same time, it was reported that up to 44% of patients showed some symptoms of the disease - apparently, these were residual effects from the initial infection or some post-infectious complications. Severe symptoms were not observed in any of these people. Attempts to cultivate the virus taken from their samples did not lead to anything, which suggests that there was apparently no viable virus in their organisms.
On the subject: What can and what can not tell a study on antibodies to COVID-19
Similar studies of a possible "secondary infection" were previously conducted in China. Their results were published this week: the average time for the disappearance of viral RNA in smears from the nasopharynx of patients was 18,5 (13,25–22) days, in sputum - 22 (18,5–27,5), in stool –17 ( 11,5–32) days. Thus, residues of RNA in the intestine can be detected almost five weeks after infection - much later than the symptoms of the disease disappear.
The first reports of the possibility of re-infection with COVID-19 appeared back in February, when a coronavirus test showed a negative result in a recovering patient from Japan, and then again became positive. Similar cases were reported in Japan and later, and then several times faced with "re-infection" in China. Scientists who were asked to comment on these situations said that although accurate information about the possibility of re-infections did not yet exist, this could be explained, in particular, by errors in test systems. Many tests for coronavirus, especially at the beginning of a pandemic, were not very accurate and yielded many erroneous, including false-positive results.
To study the issue of reinfestation in more detail, Beijing researchers conducted an experiment on model animals some time ago. Macaques were infected with COVID-19, and a few days later a high concentration of viruses was detected in their samples. Later, specific antibodies to the virus were detected in their blood. 28 days after the initial infection, two macaques were tried to infect again, but this could not be done. Five days after an attempted reinfection, no virus particles were found in smears from the nasopharynx and intestines, and further examination also showed the absence of any manifestations of the disease in these monkeys. Interestingly, in one of the monkeys, the concentration of specific antibodies to the S-protein (the receptor-binding protein of the virus, the so-called "spike") after re-infection increased more than three times, while the other remained unchanged.
Thus, now, apparently, there is no reliable data on real re-infections of COVID-19. All described cases can be explained by residual effects of the main infection or false-positive test results. Moreover, there is serious reason to believe that during the first months after the illness she simply cannot be infected again.
However, the COVID-19 pandemic began only a few months ago, and what is going to happen with the immunity of the population in, for example, a year is not yet possible to predict. The presence of antibodies in the blood after a disease, unfortunately, does not guarantee permanent immunity to infection. A lot depends on the type of disease. So, people who have had measles, chicken pox, and rubella gain life-long immunity to them, and you can get the flu many times, despite the fact that the body is exposed to infection every time and completely heals. First of all, this is due to the variability of the influenza virus: constant shuffling and changes in its structure do not allow the body to learn to develop antibodies once and for all that would act against all its variants.
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To ordinary coronavirus infections that cause seasonal colds, immunity in humans persists, as a rule, only for several months (as shown, for example, here). However, the virus that causes COVID-19 differs from them in many ways, ranging from the genome structure to the nature of the course of the disease, so nothing can be predicted for sure. Opinions of scientists on this subject are different. So, the virologist from the University of Texas at Galveston, Vinit Menaheri, suggests that immunity to the new coronavirus will remain in humans for one to two years. And the microbiologist from Ikan Medical School in New York Florian Krammer, whose developments are now actively used in the production of serological tests, believes that antibodies to COVID-19 are likely to be present in the blood for relatively short time, but in general the immune system will learn to respond to it is more effective.
As an optimistic example, we can cite the SARS-CoV-1 causative agent of SARS-CoV-2002, a coronavirus that appeared in 19 and caused people to have symptoms similar to COVID-1. According to a number of studies, immunity to SARS-6 persists for at least XNUMX years after infection, and the harder the patient suffered the infection, the higher his level of memory T-cells, which can “remember” foreign particles and react to their reappearance in the body .
